1. Field of the Invention
The present invention generally relates to rackets for use in games and, more particularly, is concerned with racket frame constructions having holes for tailoring frame stiffness.
2. Description of the Prior Art
A conventional game racket frame, such as a tennis racket frame, is ordinarily an integral structure which includes a head portion, a throat portion and a handle portion. Typically, the racket frame is fabricated of composite-type material composed of high modulus fibers such as graphite fibers or glass fibers in a matrix of an epoxy resin. Also, racket frames have been fabricated from other materials, such as aluminum, wood and plastics.
The head portion of the racket frame typically has a round or oval configuration and contains a plurality of holes aligned in a common plane for applying stringing under tension and in a grid pattern across the head portion to provide a ball striking area of the racket. The handle portion of the racket frame is usually covered with an outer sheath for facilitating gripping of the racket by the user's hand.
The above-described construction of a conventional tennis racket poses several shortcomings to achievement of ball striking accuracy. In one common constructional feature, the height of the handle portion is greater than the height of the head portion measured in a direction normal to the plane of the stringing across the head portion. This common feature contributes to inaccuracy of ball striking directional aim as a result of deflecting of the racket head portion away from the longitudinal axis of the racket in response to the ball striking the head portion stringing. Also contributing to directional inaccuracy of the ball is the difference between the natural frequency of the conventional racket and the much greater resonance frequency of a tennis ball, typically greater by a factor ranging from 2.5 to 5. In addition to deviations in ball striking accuracy caused by deflection of the head portion, a ball striking the stringing off the longitudinal axis of the racket causes torsional or twisting motion about the longitudinal axis, thus shifting the line of travel of a struck ball from the desired direction.
The prior art contains tennis racket constructions which implicitly or explicitly attempt to overcome some or all of these struck ball directional inaccuracies. Representative of the prior art are U.S. Patents to Brown (U.S. Pat. No. 2,481,075), Spenle (U.S. Pat. No. 3,633,910), Tabickman et al (U.S. Pat. No. 4,192,505), Fernandez (U.S. Pat. No. 4,436,305), Popplewell (U.S. Pat. No. 4,440,392) and Kuebler (U.S. Pat. No. 4,664,380). The approach of the Kuebler patent is to provide the maximum height (measured in a direction normal to the stringing plane) of the racket frame in a triangular or bight region of the throat portion of the frame where it intersects with the head portion and to taper the height both toward the handle portion and the head portion of the racket frame in opposite directions along the longitudinal axis of the racket.
However, there are practical limitations on how much the frame height can be increased which may restrict the utility of the approach of the Kuebler patent in overcoming the above-described inaccuracies of a conventional racket frame. One limitation is that a significant increase in frame height in the head portion, adjacent the throat portion of the frame to stiffen the head portion against deflection, has the disadvantage of increasing the amount and location of material in the racket frame and thus frame weight and balance in a corresponding fashion.
Consequently, in view of the above-described drawbacks of the approach of the Kuebler patent to overcoming the struck ball directional inaccuracies of conventional tennis racket frame construction, a need still exists for another approach which will overcome these problems without creating new ones in their place.